Intended for healthcare professionals

Clinical Review ABC of psychological medicine


BMJ 2002; 325 doi: (Published 21 September 2002) Cite this as: BMJ 2002;325:644
  1. T M Brown,
  2. M F Boyle

    Delirium is a common cause of disturbed behaviour in medically ill people and is often undetected and poorly managed. It is a condition at the interface of medicine and psychiatry that is all too often owned by neither. Although various terms have been used to describe it—including acute confusional state, acute brain syndrome, and acute organic reaction delirium is the term used in the current psychiatric diagnostic classifications and the one we will use here.

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    Sensory misperceptions, including hallucinations and illusions, are common in delirium. (Don Quixote and the Windmill by Gustave Doré, 1832-1883)

    Clinical features

    Delirium usually develops over hours to days. Typically, the symptoms fluctuate and are worse at night. The fluctuation can be a diagnostic trap, with nurses or relatives reporting that patients had disturbed behaviour at night whereas doctors find patients lucid the next day.

    Impaired cognitive functioning is central and affects memory, orientation, attention, and planning skills. Impaired consciousness, with a marked variability in alertness and in awareness of the environment is invariably present. A mistaken idea of the time of day, date, place, and identity of other people (disorientation) is common. Poor attention, and disturbed thought processes may be reflected in incoherent speech. This can make assessment difficult and highlights the need to obtain a history from a third party. Relatives or other informants may report a rapid and drastic decline from premorbid functioning that is useful in distinguishing delirium from dementia.

    Disturbed perception is common and includes illusions (misperceptions) and hallucinations (false perceptions). Visual hallucinations are characteristic and strongly suggest delirium. However, hallucinations in auditory and other sensory modalities can also occur.

    Diagnostic criteria fordelirium*

    • Disturbance in consciousness with reduced ability to focus, sustain, or shift attention

    • Change in cognition (such as memory, disorientation, speech, disturbance) or development of perceptual disturbance not better accounted for by pre-existing or …

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